In conclusion, at present, our results do not allow to recommend GLN supplementation in a generic population ofcritically ill patients. Further RCTs are needed to confirm or deny the potential protective or harmful effect of GLN in more specific cohort of patients treated in ICUs. In particular, as our data suggest that GLN given parenterally, for more than 5 days, in patients with APACHE II < 15 might have a protective role. To confirm this trend a adequately powered RCT with this inclusion criteria is deserved.